Among the tens of thousands of sites where oil and oil products are handled, such as service stations, terminals, refineries, pipelines etc., there inevitably are accidental spills and leaks where substantial quantities of liquid hydrocarbons are lost into the subsurface. In most cases this liquid descends through the soil and finally accumulates on the water table from which it must be removed.
Equipment and methods used in handling surface spills are generally of no use in subsurface situations because of the relatively small diameter of recovery wells.
The most common method of underground recovery is to drill a well, typically thirty feet or more below the water table. By pumping water from the bottom of this well, a cone-shaped depression is created on the water table with the well as the apex. The lighter floating hydrocarbon liquid then collects in the well where it is removed by a second pump located at a fixed position near the liquid surface in the well. Systems such as this are illustrated in U.S. Pat. No. 3,901,811 issued to Finch and in U.S. Pat. No. 4,273,650 issued to Solomon. To avoid creating other problems it is necessary that these systems produce water-free product. The systems are effective as long as the pump intake and the fluid interfaces, hydrocarbon/water and hydrocarbon/air, are in the proper relationship to each other. They will, however, tolerate little variation in this relationship and still remain effective. Under natural conditions a water table is seldom static. It is usually rising or falling at varying rates depending mostly on the amount of recharge water being received from precipitation. As the water table changes, so does the pumping level in a well. Each change lowers the efficiency of a fixed-position pump and necessitates frequent observation and readjustment, thus making the process a very labor-intensive operation.
The problems associated with a fixed-position well skimmer can be eliminated by using a floating skimmer which will adjust to natural changes of the water table level. Due to the different specific gravities of hydrocarbons and water any object will float higher in water than it will in hydrocarbons. This invention utilizes this principle and allows, thereby, the floating skimmer to function indefinitely without attention.